The present invention relates to a dynamic pressure bearing device used for a magnetic disk drive or the like, and to a method for manufacturing the same.
As shown in FIG. 8, a dynamic pressure bearing device is used for a magnetic disk drive or the like. The bearing has lubricating oil 7 filled in a gap between a bearing body and a shaft body that constitute a bearing unit 20.
The bearing unit 20 is constituted as follows: on a shaft 1 serving as a shaft body, a thrust flange 2 is fixed by a screw 3, the shaft 1 is inserted into a shaft body insertion hole of a sleeve 4 serving as a bearing body, and a thrust plate 5 is bonded to the sleeve 4 so as to be opposed to the thrust flange 2.
On at least one of the outer periphery of the shaft 1 and the inner periphery of the sleeve 4, a dynamic pressure generating groove is formed to constitute a radial bearing, and dynamic pressure generating grooves are formed at any two places on the end faces of the thrust flange 2, the thrust plate 5, and the sleeve 4 to constitute a-thrust bearing.
The lubricating oil 7 is injected in a gap between the bearing body and the shaft body of the bearing unit 20 configured thus to constitute the dynamic pressure bearing device.
As a method of injecting the lubricating oil 7 into the bearing unit 20, it is possible to adopt a method of injecting the lubricating oil 7 during assembly of the bearing unit 20, and a method of injecting the lubricating oil 7 after the bearing unit 20 is assembled. For example, the following method is generally used: before the shaft 1 is inserted into the sleeve 4, a prescribed amount of the lubricating oil 7 is dropped on the internal diameter of the sleeve 4, and then, the shaft 1 is inserted. Further, the following method is also generally used: after the inside of the assembled bearing unit 20 is evacuated, the end of the bearing unit 20 is dipped into the lubricating oil 7, and then, the bearing unit 20 is returned to an atmospheric pressure to inject the lubricating oil 7 into the bearing using a difference in atmospheric pressure.
However, in the method of injecting the lubricating oil 7 during assembly of the bearing unit 20, the air is prone to enter the bearing unit 20. When the entering air is expanded due to variations in temperature and atmospheric pressure, the lubricating oil 7 may leak to the outside. Moreover, motor characteristics may be degraded by the entering air. Furthermore, since the shaft 1 is inserted after the lubricating oil 7 is injected into the sleeve 4, there is a problem that it is difficult to pour the lubricating oil 7 into a screw hole 3a of the screw 3, which is used to fix the thrust flange 2 on the shaft 1.
Meanwhile, in the method of dipping the bearing unit 20 into the lubricating oil 7 after the assembled bearing unit 20 is evacuated, it is necessary to adjust an amount of the lubricating oil 7 to a prescribed amount after the lubricating oil 7 is injected into the bearing unit 20. Further, since at least the open end of the bearing unit 20 needs to be entirely dipped into the lubricating oil 7, the lubricating oil 7 which has adhered to the outer periphery of the bearing unit 20 by the dipping needs to be removed, resulting in an extremely complicated assembling process. Besides, for example, when a screw hole for attaching components is formed on a part of the bearing unit 20, it is not possible to remove the lubricating oil 7 in the screw hole, and the lubricating oil 7 is injected into the unit 20 with a larger amount than the prescribed amount, resulting in leakage or the like of the lubricating oil 7. Hence, it is not possible to obtain a satisfactory function as a product, and there is a problem that the above-described injecting methods cannot be used.
The present invention resolves the above problem and has as its object the provision of a manufacturing method of a dynamic pressure bearing device and a dynamic pressure bearing device whereby the above-described problems are solved and a proper amount of lubricating oil can be injected by using a simple process without leaving air bubbles in a bearing unit.
A method for manufacturing a dynamic pressure bearing device of the present invention in which lubricating oil is filled in a gap between a bearing body and a shaft body, the bearing body and the shaft body forming together a bearing unit, is characterized in that the bearing unit is exposed in an atmosphere of reduced pressure to evacuate air in the gap, a proper amount of lubricating oil is supplied to an open end of the gap of the bearing unit, and then, the bearing unit is released to an atmospheric air to fill the lubricating oil into the gap.
According to this configuration, it is possible to readily realize a dynamic pressure bearing device having a satisfactory motor characteristic such that lubricating oil can be filled without allowing the air to enter the bearing, and the lubricating oil does not leak to the outside even when there occur changes in temperature and atmospheric pressure.
Further, a ring-shaped concave part having a volume substantially equal to a proper amount of lubricating oil is formed at an open end of the gap of the bearing unit, and the lubricating oil is supplied into the ring-shaped concave part, so that the proper amount of lubricating oil can be readily supplied without short or excessive supply.
Further, a plurality of bearing units are placed on a pallet, and the pallet and a lubricating oil supply side are relatively moved to continuously supply the lubricating oil to the bearing units, thereby remarkably improving production efficiency.
Besides, since a dispenser having a nozzle applied with an oil repellent agent on a leading end thereof is used to supply lubricating oil, even in continuous lubrication of the lubricating oil, it is possible to prevent excessive adherence of the lubricating oil to the leading end of the nozzle, thereby accurately supplying the lubricating oil to the bearing unit.
A dynamic pressure bearing device of the present invention, in which lubricating oil is filled in a gap between a bearing body and a shaft body of a bearing unit having one end closed and the other end opened, is characterized in that a ring-shaped concave part having a volume substantially equal to a proper amount of oil is formed at an open end of the gap.
According to this configuration, since a prescribed amount of lubricating oil is filled in the bearing unit without allowing entry of air bubbles, it is possible to provide a device having a satisfactory motor characteristic.
Further, the ring-shaped concave part is formed at least in one of the shaft body and the bearing body, or the ring-shaped concave part may be constituted by a chamfered part formed all around an opening of a shaft body insertion hole of the bearing body, the chamfered part being positioned at the open end of the gap of the bearing unit, and a space formed at a position connected to the chamfered part and extending to a point where an outer periphery of the shaft body and an inner periphery of the bearing body are close to each other, whereby a sum of a chamfered volume of the chamfered part and a volume of the space is made substantially equal to the proper amount of lubricating oil. In addition, when ring-shaped grooves are formed on an open side of the bearing unit in order for preventing a spread of lubricating oil, it is possible to readily drop the prescribed amount of lubricating oil without causing adherence of the lubricating oil more than necessary onto the open end of the bearing unit.